It’s called the Sahara Pump theory. Wiki has a good intro.
Happy to oblige. 
The oldest fossil identified as H. sapiens is 195,000 years old.
But you’re right. The generally accepted date is 200,000 years.
So very true.
True, just as there were people in Britain before the Celts, but there were subsequent major migrations into the area.
One thing every human society likes to do is gossip. I imagine that in a society of three people, they’d come up with names so they could talk about the third one behind her back.
It’s been estimated (in Guns, Germs, and Steel) that humans spread from the Bering Land Bridge to the tip of South America in 1000 years or less.
Given that the first multicellular life is believed to have exploded to fill an essentially empty world in certainly less than 5 million years (probably less than 2 million years, and Stephen Jay Gould has argued for much less time than that) it seems to me we probably spread very quickly. The more interesting question may be, what took us so long to get started? Why did we stay in the Rift Valley for so long?
“We” didn’t stay in the rift valley. As Mr Dibble already noted, modern humans were in Southern Africa over 100k years ago. As for modern humans taking a long time to leave Africa, one reason might be very low population densities. There is strong evidence that we went through a population bottleneck about 75kk years ago. There might have only been a few thousand of us around.
Pre-modern hominids as well. People think of East Africa because that’s where African hominid studies got started, but the Rift Valley was neither the be all nor end all of human evolution in Africa - new discoveries have been coming from Southern Africa ever since Taung, and I think other, equally exciting discoveries are waiting in the rest of Africa, especially the Sahara/Sahel areas.
After evolving 200,000 years ago, is what I was getting at. But that’s because I’m a a believer in the rapid expansion – I have trouble imagining it took 100,000 years to spread to South Africa if it only took 1,000 to go the length of North and South America, so I was inclined to believe we didn’t start spreading for a while.
I didn’t mean to imply that we were in Southern Africa only starting about 100k years ago. In fact, I’m not really familiar with the details of the fossil record there re: modern humans. It’s thought that we developed the lifestyle of “beach combing” in Southern Africa, and that’s what helped us hug the coasts as we spread out of Africa. But it wouldn’t surprise me if the fossil record from 15k years ago in South America is better preserved than that of 150k years ago in Southern Africa.
Ancient fragment of finger bone suggests humans travelled east from Africa earlier than thought
An ancient fragment of human finger bone found in the Saudi Arabian desert suggests that mankind ventured east out of Africa 30,000 years earlier than thought.
The scrap of bone, measuring little more than an inch long, had lain undiscovered for up to 90,000 years.
Its discovery potentially revolutionises our understanding of early human history, challenging a long-held consensus that humans started to move en masse into Eurasia in a single wave about 60,000 years ago.,…
Meh, we already had results indicating that the Basal Eurasians split from the rest of the out-of-Africa lot 80 000 years ago, so we kindof knew that. Also, we’ve found fairly anatomically modern remains in Morocco dating back 300 000 years. So I think a lot of the excitement is due to our modern concept of “Africa”. I mean its a straight line along mostly coast in the same climate zone and probably much the same ecology. 220 000 is enough to walk quite a ways.
This thread did its thing in 2010. Quite apart from Leo Bloom’s waggling finger pointing out how much we dont know, its instructive to see just how much that was considered to be the orthodoxy in human evolution has had to be updated, particularly by more comprehensive genomic studies in less than a decade.
That makes me nervous when so many people still seem to fixate on what they were taught at school (or think they remember) and assume it remains the state of play about human evolution, our genetic diviersity, the validity of races etc etc twenty, thirty or more years on. If there is one area of science where things change rapidly and in ways that affect the big picture of our knowledge, its in the study of human evolution.
I think pretty much everyone agrees that race is still a stupid concept applied to todays populations. Might have more validity when speaking of ancient hominids. Otherwise… stuff that was orthodox 3 moths ago might be outdated:) It is an exciting time if you are interested in these things.
As is the case in many disciplines of science, the concept of Orthodoxy has become quite unorthodox.
Sent from my SM-N910V using Tapatalk
And now it’s 195,008 years old 
I taught science for many, many years, and had a sign posted in the front of the room that said, “…As far as we know.” We had many interesting discussions about that and I used to hope that kids developed the notion (somewhat unsettling as it is for them) that what we “know” is only so up to this point in the history of the universe. In some ways, I hoped that they would then be motivated go out in the world set upon finding new truths.
I love that. It encourages students to know more than their teachers know.
Sent from my SM-N910V using Tapatalk
it began with the advent of 2 Hominids & a Truck.
The real question is not “Why?” but rather “When?”. I ask this about a year ago: When did modern humans leave Africa?, and the best answer was about 88,000 years ago based on genetics.